The pollution of rivers, lakes, swamps, and seas is attributable to foul liquid wastes from factories, individual dwellings, restaurants, assembly halls, etc., and treatment apparatus for purifying such foul liquid waste into clear water by the activity of micro-organisms living in sludge have been used heretofore. Thus the present invention also relates to an improved method and apparatus for purifying a mixed foul liquid waste of human body wastes (fecal matter and urine) and miscellaneous liquid wastes discharged from the above places by the activity of micro-organisms.
In general, the treatment processes of foul liquid wastes include primary and secondary treatment processes, etc. According to the present invention, a sedimentation tank is used for the primary treatment process in which heavy, relatively large foul matter and dust are settled, and a submerged bioaeration-beds tank is used for the secondary treatment process in order to make the supernatant liquid separating out in the sedimentation tank purer and clearer. The apparatus for the secondary treatment process plays an important role; that is, the superiority or inferiority of its function determines the purification efficiency of the whole plant.
A thorough investigation of secondary treatment apparatus carried out by the present inventor has led to the invention for the following unique submerged bioaeration-beds tank. In the submerged bioaeration-beds tank, according to the present invention, a plurality of rectangular irrigated or medium sheets which are made of plastics, especially of polyvinyl chloride, or of asbestoscement and which form the bases for developing biomembranes are horizontally positioned parallel to one another at regular intervals above one another. According to the investigation carried out by the present inventor, the multiplication and activity of micro-organisms scarcely depend on the kind of the material of which the irrigated or medium sheets are made. The upper irrigated or medium sheet is mounted at its both sides and one end in close contact with three tank walls and a gap of several cm is formed between the other end and the remaining opposite tank wall. A gap is formed between the next irrigated or medium sheet and the opposite tank wall. Thus, the irrigated or medium sheets are staggered down through the tank to form gaps in a zigzag manner. The foul liquid waste from the sedimentation tank is charged at one end of the upper irrigated or medium sheet. The charge flows to the gap at the other end of the sheet where it falls to the next irrigated or medium sheet. Here it flows in the opposite direction to the gap on the opposite side from which it falls to the next irrigated or medium sheet. This continues down the bioaeration-beds tank to the bottom. In practice, the foul liquid waste fills the tank. The tank is equipped with air-lift pumps whereby the foul liquid waste is raised from the bottom section to the upper section and recirculated through the spaces between the individual irrigated sheets in a zigzag manner, as mentioned above.
A description will now be set forth as regards the activity of micro-organisms living in sludge. In the above-described submerged bioaeration-beds tank, when air is supplied by means of the air-lift pumps and oxygen is mixed therewith, and dissolved into the foul liquid waste by the agitation of small air-bubbles, allowing aerobic bacteria contained in the foul liquid waste to respire and promoting their multiplication, the micro-organisms thus adhere to the irrigated or medium sheets to form biomembranes. The microorganisms multiply more and more by adsorbing and taking in the polluting matter contained in the foul liquid waste and exert their excellent purifying activity.
During this process the foul liquid waste is rapidly purified into clear water. It is for the purposes of generating as many biomembranes as possible by increasing the surface area and of improving the purification efficiency that the irrigated or medium sheets forming the bases for developing biomembranes are made laminar. In the submerged bioaeration-beds tank according to the present invention, the reason why the irrigated sheets are mounted horizontally and parallel to one another is to grow the biomembranes in a stable state and at the same time to make contact between the foul liquid waste and biomembranes adhering to both sides of each irrigated or medium sheet over and over again. Therefore, the foul liquid waste turbulently flowing into the tank comes in contact with the biomembranes during its circulation and recirculation from top to bottom and from bottom to top. On the other hand, the utilization of settlement action caused by gravity during the flowing of the foul liquid waste leads both to the promotion of the adsorption on the biomembranes and to the improvement in purification efficiency. As the results of these, suspended solids and sludge are hardly produced, and both B.O.D. (Biochemical Oxygen Demand) and C.O.D. (Chemical Oxygen Demand) are extremely low, which means excellent purification efficiencies. The reason why sludge is hardly produced is considered to be that the special bacteria within the bodies of the biomembranes adhering to the irrigated or medium sheets live on the biomembranes and that thus the multiplication of the bacteria balances with that of the biomembranes. Extremely low suspended-solids content is attributable to the facts that the biomembranes have a much greater adsorptive power and that the micro-organisms prey satisfactorily upon suspended solids. A microscopic examination of the biomembranes shows more fully that Vorticella and Opercularia representative of aerobic bacteria propagate in great quantities. Philodina and Podophrya representative of the bacteria preying upon biomembranes (bacteria) also coexist with the above-mentioned bacteria. Since biological activities are great, as stated above, enlarged irrigated or medium sheets facilitate both the improvement in purification capacities and the attainment of the effluent's B.O.D. of less than 10 p.p.m. This apparatus is applicable to any large-scale treatment, if enlarged.